Gloss & Appearance

Haziness

Similar to 'Sheen', haziness is more correct termed the 'Definition of Image' of a coating and is a measure of the clarity of the reflection, or 'mirror-like' finish of the coating.  This attribute is usually confined to gloss coatings.

Pre-Cure

Appearance looks uneven and broken before curing.

  • Potential Cause

    Back ionisation occurring.  Where voltage is too high, or where the gun nozzle is too close to the part the powder layer reaches a saturation point, beyond which additional coating is deflected off the surface and eventually causing the deposited film to jump off the part, creating craters and star-like patterns in the powder film.

  • Solution

    Check the electrical earth and that the grounding points are clean.  Decrease the voltage by 10-20 kV.  Move gun further away from component.

Clouding

Uneven light to dark or matt to glossy effect of the coating on the substrate

  • Potential Cause

    Spray gun settings:

    • Gun distance from part too great or small
    • Uneven powder transport
    • Poor charging
    • Poor electrical earth.

  • Solution

    Test and optimise gun settings

  • Potential Cause

    Micropinholing from gassing caused by

    • moisture in the local environment, airline or substrate;
    • a porous substrate.

  • Solution

    Ensure that humidity levels are controlled and that the air line is clean and dry.  Check that the substrate has not trapped air or moisture by pre-heating it slightly above the curing temperature of the coating, allowing to cool then powder coating.

Blooming

Haze like film on the surface, which can be wiped off.

  • Potential Cause

    By-products of resin manufacture depositing on surface because their energy is too low to sublime off the substrate. Caused by

    • Oven curing temperature too low
    • Heavy substrates
    • Prolonged exposure to elevated temperatures, in particularly ~150-160 Celsius.

  • Solution

    Ensure metal temperatures reach the recommended curing temperature. Whilst coatings will cure at reduced temperatures when given a longer cure, this may cause severe blooming.  Do not leave products to cool in a box oven. Once the curing cycle is complete, open the oven doors and remove the work.

  • Potential Cause

    Insufficient air circulation in the oven

  • Solution

    Increase air circulation

  • Potential Cause

    Contamination on the surface because of incompatible powder coatings from different manufacturers

  • Solution

    Use only powder coatings from one manufacturer at the same time in an oven.  Contact us.

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